Rigid-rod Molecules Research Articles

Design and Evaluation of a Reprocessable Bismaleimide Thermoset: Enhancing Functionality and Sustainability Compatibility.

Bismaleimide (BMI) resins are high-performance thermosets that are primarily used in aerospace because of their exceptional heat resistance and physical properties. However, their growing demand has led to significant environmentally unfriendly waste. To address this, our research proposes a reprocessable BMI system using a newly synthesized BMI vitrimer (BMIV) with functional groups that form covalent adaptable networks (CANs). To enhance the properties, a symmetrical BMI with two ester groups introduced into the rigid rod molecule was designed as a CAN component. After confirming the structure using various spectroscopic techniques, BMIV was coupled with aromatic diamines via an additional aza-Michael reaction to obtain the cured resins. Subsequently, the mechanical properties and reprocessing behavior of the thermally stable and optimized thermosetting material with the best performance were evaluated, and the evidence, mechanism, and activation energy of the topology rearrangement are reported in detail.

Size dependence of transport coefficients of thin and long asphaltene molecules as determined using a mode-coupling theory approach

Rotational diffusion coefficients (Dr) and viscosities (η) of rigid rod molecules consisting of N beads were first revisited for the situation at low density. Starting from this, the transport coefficients at high density condition were expressed in terms of different density pair correlation functions, such as intermolecular radial distribution function and structure factor. This was attained using a mode-coupling theory approach to approximate the intermolecular force–force correlation function, and thus the friction coefficient. As these density pair correlation functions are dependent on N, they determine how “entangled” the rigid rod molecules are, and therefore reproducing the crossover in the log –log plot of transport coefficients with N. It was found that there are crossovers in transport coefficients from Dr∼N−2.3 and η∼N2.3 at low N to Dr∼N−6.5 and η∼N6.5 at high N. The strength of N dependence is mainly determined by the competition between available free space and the compressibility of the system.

Structure and Conformation of Hydroxypropylmethyl Cellulose with a Wide Range of Molar Masses in Aqueous Solution─Effects of Hydroxypropyl Group Addition.

The structure of hydroxypropylmethyl cellulose (HpMC) samples with a wide range of weight average molar masses (Mw) from 23 to 5000 kg mol-1, a controlled degree of substitution (DS) of 1.9 by methyl groups, and a molar substitution number (MS) of 0.25 by hydroxypropyl groups dissolved in aqueous solution was examined using static light scattering (SLS), dynamic light scattering (DLS), small-to-wide angle neutron scattering (S-WANS) techniques, and intrinsic viscosity ([η]) measurements. The determined Mw and the radius of gyration (Rg) showed the relationships Rg ∝ Mw1.0 and [η] ∝ Mw1.7 in a range of Mw < 100 kg mol-1, similar to rigid rod molecules in solution. However, exponents in the relationships decreased gradually with increasing Mw and reached ∼0.5 in a high Mw region, which is a typical value of flexible chain molecules for both Rg and [η]. These observations suggest that the HpMC samples behave as semiflexible rods with a certain persistence length (lp). The ratios of the hydrodynamic radius via DLS measurements to Rg also supported semiflexible rod behavior. Particle form factors and the average lengths (L) resulting from SLS and S-WANS experiments are well described with rigid rod particles in the range of Mw < 100 kg mol-1 and semiflexible rods with lp ∼ 100 nm in Mw > 100 kg mol-1. Because the average contour length (lc) calculated from Mw is approximately twice as long as L in the Mw range < 100 kg mol-1, the formed HpMC particles possess a folded hairpin-like elongated rigid rod structure. However, the lc/L value increases gradually in the range Mw > 200 kg mol-1, where the formed HpMC particles behave as semiflexible rods. The formed particle structure was substantially different from that found in methyl cellulose samples with a similar DS value, which showed rod-like behavior over a wide Mw range. The addition of hydroxypropyl groups only at MS = 0.25 effectively changed the formed particle structure.

Research progress in molecular dynamics of high-performance PBO fibers

This article reviews the application and development of molecular dynamics in the field of poly(p-benzobisoxazole) (PBO) molecules, including the use of molecular dynamics simulations to calculate the theoretical Young’s modulus of PBO molecules and discuss them from the perspective of molecular theory Combine the rotational isomerism state theory with the long molecular dynamics simulation of small fragments to evaluate the limit length of the persistence vector a. The molecular dynamics calculation is used to study the molecular motion behavior of isolated rigid rod molecules such as PBO. Combining computer simulation technology and X-ray diffraction data collected by the imaging board system to analyze the crystal structure of the PBO fiber, and use molecular dynamics and dynamic modeling to establish the PBO/epoxy interface and study its performance.

Synthesis of Rigid Rod, Trigonal, and Tetrahedral Nucleobase-Terminated Molecules

AbstractAn efficient fragment splicing method for the construction of multiple nucleobase-terminated monomers has been developed. Conformationally fixed rod, trigonal planar and tetrahedral thymine and adenine structures were generated in moderate to good yields, which will serve as inspiring examples for exploration of nucleobases as natural hydrogen-bond components in supramolecular chemistry.

Characterisation of the molecular properties of scleroglucan as an alternative rigid rod molecule to xanthan gum for oropharyngeal dysphagia

Scleroglucan, a neutral β(1–3) glucan with β(1–6) glucan branches every third residue, is being considered as an alternative rod-like, shear thinning high molecular weight β-glucan based polysaccharide to xanthan gum for the management of patients with oropharyngeal dysphagia. It is therefore important to understand more fully its hydrodynamic properties in solution, in particular heterogeneity, molecular weight distribution and its behaviour in the presence of mucin glycoproteins. A commercially purified scleroglucan preparation produced by fermentation of the filamentous fungus Sclerotium rolfsii was analysed in deionised distilled water with 0.02% added azide. Sedimentation velocity in the analytical ultracentrifuge showed the scleroglucan preparation to be unimodal at concentrations >0.75 mg/ml which resolved into two components at lower concentration and with partial reversibility between the components. Sedimentation coefficient versus concentration plots showed significant hydrodynamic non-ideality. Self-association behaviour was confirmed by sedimentation equilibrium experiments with molecular weights between ~3 × 106 g/mol to ~5 × 106 g/mol after correcting for thermodynamic non-ideality. SEC-MALS-viscosity experiments showed a transition between a rod-shape at lower molar masses to a more flexible structure at higher masses consistent with previous observations. Sedimentation velocity experiments also showed no evidence for potentially problematic interactions with submaxillary mucin.

Radical Polymerization of Pendant (Meth)acrylates on a Rigid Helical Polyisocyanate Backbone Producing Poly(meth)acrylates with “Ideally” Atactic Main Chain Configuration

This study includes a topic that poly(methyl methacrylate) (PMMA) with an “ideally” atactic main chain configuration, approximately triad tacticities of mm/mr/rr = 1/2/1, has been produced in solution by the “one-dimensionally regulated” radical polymerization using rigid helical polyisocyanate as a macromolecular template. Three types of isocyanate monomers with pendant (meth)acryloxy groups, such as 2-(methacryloxy)ethyl isocyanate (MOI), 2-[2-(methacryloxy)ethoxy]ethyl isocyanate (MOI-EO), and 2-(acryloxy)ethyl isocyanate (AOI), were polymerized using a titanium alkoxide complex to produce the corresponding polyisocyanates, MOI-n, MOI-EO-n, and AOI-n, respectively, in which n represents the number-averaged degree of polymerization. From the SAXS measurements of MOI-26 in hexafluoro-2-propanol and MOI-EO-38 in tetrahydrofuran at 25 °C, the polyisocyanates were found to be considered as rigid rod molecules. The radical polymerization of the pendant (meth)acryloxy groups was performed, and the polyisocyanate template was removed by alkali hydrolysis followed by methyl esterification, eventually producing the poly[methyl (meth)acrylate]s. The diad, triad, and pentad tacicities of the products were determined by the 1H and 13C NMR spectra, and these probabilities followed those calculated based on the Bernoulli statistics. The influences of the polymerization conditions, such as polymerization temperature and monomer concentration, on the tacticity of the final polymers were clarified. The effect of the flexible spacer between the polymerizable group and polyisocynate template was also evaluated. The radical polymerizations in which the polymerizable groups are molecularly regulated on a rod-like helical polyisocyanate backbone produced vinyl polymers with inimitable tacticities even in the solution state.

Interfacial Adhesive Properties between a Rigid-Rod Pyromellitimide Molecular Layer and a Covalent Semiconductor via Atomistic Simulations

We conducted a comprehensive atomistic simulation study of the adhesive properties of aromatic rigid-rod poly-[(4,4'diphenylene) pyromellitimide] on a dimer-reconstructed silicon surface. We describe the structural developments within the adherent's interfacial region at the atomistic scale, and evaluate the energetics of the adhesive interactions between bimaterial constituents. In particular, we observe a transition between noncontact and contact adhesion regimes as a function of the interfacial bonding strength between the polyimide repeat units and the silicon substrate. This transition is manifest by a three- to four-fold increase in adhesive energy, which is entirely attributable to structural relaxation in the organic layer near the interface, revealing the importance of accurately describing structural details at interfaces for reliable interfacial strength predictions. The underlying molecular reconfigurations in the pyromellitimide layer include preferred orientation of the rigid-rod molecules, molecular stacking, ordering, and the local densification. The role of each of these factors in the adhesive behavior is analyzed and conclusively described. Where possible, simulation results are compared with theoretical model predictions or experimental data.

Micro-macro numerical simulation of rod-like polymeric solutions

利用微宏观耦合方法模拟了棒状分子聚合物溶液在平板Couette流动中的复杂流变行为，其中微宏观模型通过非均匀Doi理论来描述.数值模拟中，应用有限体积方法耦合求解了介观尺度上的Smoluchowski方程和宏观尺度上的流场守恒方程.数值结果不仅得到了若干种典型的流动类型，而且还预测了另外两种新的复合瑕疵结构.数值试验表明：棒状分子聚合物的流变结构主要依赖于De数、分子相对尺度以及溶液浓度常数的取值；并且De数对分子指向矢的翻滚周期、随流取向角等微观特性也均有明显影响.

Synthesis of Hybrid Masked Triyne−Phenylene Axial Rods Containing (E)-β-Chlorovinylsilanes in the π-Conjugated Framework

A two-directional synthesis of a masked hexayne 7, in which two beta-chlorovinylsilanes protect two of the internal alkynes, is reported. The key step involves the Pd-catalyzed oxidative dimerization of alkyne 10 to provide diyne 12, which is elaborated into centrosymmetric masked hexayne 7 in four steps. Masked hexayne 7 is a constitutional isomer of masked hexayne 2, which has been used as a monomer unit for oligoyne assembly. Although masked hexayne 7 was not as convenient a building block as 2 for application in oligoyne assembly, one of its precursors, namely alkyne 10, could be used successfully in Sonogashira couplings, which allowed the incorporation of aromatic spacers and the formation of hybrid masked triyne-phenylenes 20 and 28. Compounds 20 and 28 both contain removable end-groups, which will permit their application as building blocks for the assembly of classes of long-chain, pi-conjugated rod-like molecules. Rod-like molecule 34, which possesses a similar conjugated scaffold as 28, was also prepared by using a similar strategy. Treatment of 34 with TBAF effected a 2-fold dechlorosilylation to provide a rigid rod molecule 35 in which two phenylene units interrupt an octayne scaffold.

Poly(aryleneethynylene)s

Poly(aryleneethynylene)s (PAE) are easily synthesized, chemically stable, and color-responsive towards their surroundings. These superbly chromic polymers are attractive as active transducers in sensors and advanced organic electronic devices. PAEs are generally fluorescent with emission maxima ranging from 420-600 nm, and can be either water- or organo-soluble. PAEs from linear building blocks are rigid rod molecules and display a host of supramolecular arrangements in solution and in the solid state. The poly(para-phenyleneethynylene)s (PPE) are lyotropic or thermotropic smectic liquid crystalline. In the solid state, PPEs display lamellar supramolecular structures that lead to distinct stranded nanoscale morphologies. The spectroscopy and the optical properties of the PAEs and in particular of the PPEs are dominated by their conformation, which is influenced by solid-state packing, solvent, temperature and other factors. The presence of twisted and planar forms and their interconversion leads to attractive structure/property relationships; PAEs are of use as ingredients for advanced supramolecular materials.

Design of Porphyrin Nanoclusters toward Discovery of Novel Properties and Functions

Abstract We have designed a variety of functional metalloporphyrin nanoclusters, connected via covalent or noncovalent linkages, since a discovery of fused bismetalloporphyrins [Ar3P]2(II) and [Ar3P]2(III) (Schemes 1–10 include symbols of the compounds), which have a strong π-electronic interaction over the bisporphyrin array. Among them, the following three topics are described in this review article. (1) Fused porphyrin nanoclusters: Directly fused oligoporphyrins, obtained through oxidative fused reactions of metalloporphyrins, show extremely strong π-electronic communications among the multiporphyrin components. (2) Self-assembled porphyrin nanoclusters: A zinc complex of meso–meso linked bisporphyrin [PyP]2(I) bearing 4-pyridyl substituents, which allow Zn–N coordination interaction, forms a homochiral box-shaped cyclic tetramer {[PyP]2(I)}4. Its rotamers upon insertion of an oligoalkynylene bridge between the two porphyrin components [PyP]2(≡)n (n = 1, 2, and 4) result in “conformational solvatochromism in nonpolar solvents” in n = 2 and “chiroptical sensing of asymmetric hydrocarbons” in n = 4, due to molecular recognition of solvents at the nanoscale cavity of box-shaped architecture. While a zinc porphyrin bearing a 3-pyridyl substituent (3-Py)P forms a cyclic tetramer with considerable structural distortion, its π-extended derivative (3-Py)P(≡)1 bearing a trimethylsilylethynyl group shows “supramolecular thermochromism” with a vivid color change, due to a temperature-dependent self-assembling event. A supramolecular polymer of J-aggregated zinc porphyrin dendrimer DP can visualize chiroptically a macroscopic chirality of vortex flows, generated by mechanical rotary stirring of a fluid. (3) Inorganic–organic nanocomposites: A giant ring-shaped polyoxomolybdate cluster MC having a large cavity with a diameter of approximately 2.3 nm accommodates up to three molecules of aminophenyl-substituted metalloporphyrins TAP via hydrogen-bonding interactions, resulting in formation of discrete inorganic/organic inclusion complexes. Template-assisted cofacial assembly of MC by an oligomeric p-phenylenebutadiynylene rigid rod molecule bearing ammonium ion pendants PBn allows formation of an inorganic/organic one-dimensional (1D) nano-object, having a polypseudorotaxane structure.

Rheological phase diagrams for nonhomogeneous flows of rodlike liquid crystalline polymers

The rheological phase diagrams for solutions of rigid rod molecules are computed for planar Couette and Poiseuille flow as a function of Deborah number, initial orientation, and wall separation; this analysis extends the seminal work of Larson and Öttinger [R.G. Larson, H.C. Öttinger, Effect of molecular elasticity on out-of-plane orientations in shearing flows of liquid-crystalline polymers, Macromolecules 24 (1991) 6270–6282] to nonhomogeneous flows. The Doi diffusion equation is solved by using a finite-element discretization of the rod distribution function and Onsager interaction potential. Simulations of planar Couette flow show the familiar logrolling–tumbling–wagging–flow-aligning cascade as Deborah number increases, and the critical Deborah numbers associated with transitions between states vary with wall separation. Defects are caused solely by wall interactions rather than artificial anchoring conditions. Simulations of planar Poiseuille flow show that the system tends toward either logrolling states or composite flow-aligning/logrolling attractors depending on the Deborah number, wall separation, and initial orientation.

Artificial tongues and leaves

Abstract The objective with synthetic multifunctional nanoarchitecture is to create large suprastructures with interesting functions. For this purpose, lipid bilayer membranes or conducting surfaces have been used as platforms and rigid-rod molecules as shape-persistent scaffolds. Examples for functions obtained by this approach include pores that can act as multicomponent sensors in complex matrices or rigid-rod π-stack architecture for artificial photosynthesis and photovoltaics.

Aqueous self-assembly of aromatic rod building blocks

One of the most fascinating subjects in areas such as nanoscience and biomimetic chemistry is concerned with the construction of novel supramolecular nanoscopic architectures with well defined shapes and functions. Supramolecular assemblies of aromatic rod molecules provide a facile entry into this area. Aromatic rigid rod molecules consisting of hydrophilic flexible chains, in aqueous solution can self-assemble into a variety of supramolecular structures through mutual interactions between aromatic rod molecules and water, including hydrophobic and hydrophilic interactions and pi-pi interaction. The supramolecular architecture in water can be manipulated by variation of the shape of the rigid segments, as well as the relative volume fraction of the flexible segment. The rigid aromatic segments have significant photonic and electronic properties. The self-assembly of aromatic rod molecules in water, therefore, can provide a strategy for the construction of well-defined and stable nanometer-size structures with chemical functionalities and physical properties as advanced materials for photonic, electronic and biological applications.

Layer Spacing of Montmorillonites Modified with Rigid Rods

The dependence of the interlayer distance in modified montmorillonite clays on the length of rigid rod molecules used for clay organophilization is studied. Therefore, a series of fully aromatic compounds of different length functionalized with a terminal amine group has been synthesized and transformed into the corresponding ammonium salts. The interlayer distance is determined by X-ray diffraction, the quantity of the modifier incorporated in the clay is obtained by thermogravimetric analysis. It is shown that the distance between layers in the modified clay does not depend on the length of the modifier used. This fact leads to the conclusion that rigid rods must be oriented parallel to the clay layers. On the other hand, the molar percentage of modifier molecules incorporated in the clay structure depends on the length of the rigid rods in the sense that shorter molecules are considerably easier to incorporate than longer ones.

Synthetic Multifunctional Nanoarchitecture in Lipid Bilayers: Ion Channels, Sensors, and Photosystems

Abstract The creation of functional materials such as ion channels, porous sensors, or smart photosystems depends critically on our ability to assemble sophisticated, error-free and self-repairing nanoarchitecture in a predictable manner. To address these challenging topics, we often used lipid bilayer membranes as compartmentalizing platform and have introduced rigid-rod molecules as privileged scaffolds that bypass all folding problems because they do not fold. This approach provides access to motifs such as rigid-rod barrels, helices, stacks, slides, and wires that can act as smart, stimuli-responsive photosystems, pores, ion channels, hosts, sensors, and catalysts. The selected examples focus on naphthalenediimides (NDIs), a compact, organizable, colorizable, and functionalizable n-semiconductor. This versatile module is used in rigid-rod molecules to mediate transmembrane anion transport by anion–π interactions, as sticky π-clamp within pore sensors to catch otherwise elusive analytes by aromatic electron donor–acceptor interactions, or in blue, transmembrane π-stack architecture to collect and convert photonic energy. These specific examples with multifunctional NDI nanoarchitecture are of help to outline, on the one hand, possibilities to contribute to advanced functional materials such as multianalyte sensors or solar cells and, on the other hand, to keep on wondering about an enormous structural and functional space waiting to be explored.

Cooperative light-induced molecular movements of highly ordered azobenzene self-assembled monolayers

Photochromic systems can convert light energy into mechanical energy, thus they can be used as building blocks for the fabrication of prototypes of molecular devices that are based on the photomechanical effect. Hitherto a controlled photochromic switch on surfaces has been achieved either on isolated chromophores or within assemblies of randomly arranged molecules. Here we show by scanning tunneling microscopy imaging the photochemical switching of a new terminally thiolated azobiphenyl rigid rod molecule. Interestingly, the switching of entire molecular 2D crystalline domains is observed, which is ruled by the interactions between nearest neighbors. This observation of azobenzene-based systems displaying collective switching might be of interest for applications in high-density data storage.

Characterization of Rodlike Poly(n-hexyl isocyanate) Macromonomers and Their Polymacromonomers by Light Scattering, SAXS, Intrinsic Viscosity, and Scanning Force Microscopy

SEC-MALS, small-angle X-ray scattering (SAXS), and viscosity measurements were made on tetrahydrofuran (THF) and n-hexane of a series of 4-vinylbenzyl and methacrylate ended poly(n-hexyl isocyanate) (PHIC) macromonomers (VB-HIC-n and MA-HIC-n, where n is a degree of polymerization of HIC and in a range from 21 to 192), together with higher molecular weight PHIC chains than the macromonomers. The molecular weight dependence of z-average mean-square radius of gyration z and intrinsic viscosity [η] of the macromonomers and PHIC chains in THF at 25 °C were quantitatively described by the wormlike chain model with the stiffness parameter (λ−1)=63nm, the molecular weight per unit contour length (ML)=725 nm−1, and the hydrodynamic diameter (dB)=1.6 nm. The SAXS scattering profile of VB-HIC-57 in n-hexane at 25 °C was also perfectly described in terms of the straight cylinder model. The results imply that the macromonomers may be regarded as a rigid rod molecule in THF and n-hexane. Cylindrical brushes consisting of polystyrene as a main chain and PHIC chains as a side chain were prepared by homopolymerizations of VB-HIC-46 and their dimensional properties were investigated in THF at 25 °C by SAXS and SEC-MALS measurements. The molecular weight dependence of z of the brushes was quantitatively explained by the wormlike cylinder model with the parameters of λ−1=48 nm, ML=2.40×104 nm−1, the cross-sectional radius of gyration of the cylinder o1/2=4.66 nm, and the end effect (δ=16.7 nm) arising from side chains near the main-chain ends. It was concluded, therefore, that the main chain stiffness of the brush remarkably increases by the presence of densely located rodlike side chains. Direct observation of single brush of the poly(VB-HIC-46) deposited on a mica was made by scanning force microscopy (SFM) to reveal the cylindrical brushes consisting of rodlike side chains with ca. 15 nm in a thickness.

Synthesis, DNA Affinity, and Antiprotozoal Activity of Linear Dications: Terphenyl Diamidines and Analogues

Diamidines 10a-g and 18a,b were obtained from dinitriles 9a-g and 15a,b by treatment with lithium trimethylsilylamide or upon hydrogenation of bis-O-acetoxyamidoximes. Dinitriles 9a-g were prepared via Suzuki reactions between arylboronic acids and arylnitriles. Potential prodrugs 12a-f and 17 were prepared via methylation of the diamidoximes 11a-f and 16a. Significant DNA affinities for rigid-rod molecules were observed. Compounds 10a, 10b, 10d, 18a, and 18b show IC50 values of 5 nM or less against Trypanosoma brucei rhodesiense (T. b. r.) and 10a, 10b, 10e, 18a, and 18b gave similar ones against Plasmodium falciparum (P.f.). The dications, 10a, 10d, 10f, and 10g are more active than furamidine in vivo. The prodrugs are only moderately effective on oral administration. Mouse liver microsome bioconversion of the methamidoxime prodrugs is significantly reduced from that of pafuramidine and suggests that the in vivo efficacy of these prodrugs is, in part, due to poor bioconversion.